An Intact NF-kappaB Pathway is Required for Histone Deacetylase Inhibitor Induced G1 Arrest and Maturation in U937 Human Myeloid Leukemia Cells

Dual-Targeted Therapy Circumvents Non-Genetic Drug Resistance to Targeted Therapy

The introduction of various targeted agents into the armamentarium of cancer treatment has revolutionized the standard care of patients with cancer. However, like conventional chemotherapy, drug resistance, either preexisting (primary or intrinsic resistance) or developed following treatment (secondary or acquired resistance), remains the Achilles heel of all targeted agents with no exception, via either genetic or non-genetic mechanisms. In the latter, emerging evidence supports the notion that intracellular signaling pathways for tumor cell survival act as a mutually interdependent network via extensive cross-talks and feedback loops. Thus, dysregulations of multiple signaling pathways usually join forces to drive oncogenesis, tumor progression, invasion, metastasis, and drug resistance, thereby providing a basis for so-called “bypass” mechanisms underlying non-genetic resistance in response to targeted agents. In this context, simultaneous interruption of two or more related targets or pathways (an approach called dual-targeted therapy, DTT), via either linear or parallel inhibition, is required to deal with such a form of drug resistance to targeted agents that specifically inhibit a single oncoprotein or oncogenic pathway. Together, while most types of tumor cells are often addicted to two or more targets or pathways or can switch their dependency between them, DTT targeting either intrinsically activated or drug-induced compensatory targets/pathways would efficiently overcome drug resistance caused by non-genetic events, with a great opportunity that those resistant cells might be particularly more vulnerable. In this review article, we discuss, with our experience, diverse mechanisms for non-genetic resistance to targeted agents and the rationales to circumvent them in the treatment of cancer, emphasizing hematologic malignancies.

Diverse Epigenetic Regulations of Macrophages in Atherosclerosis

Emerging research on epigenetics has resulted in many novel discoveries in atherosclerosis (AS), an inflammaging-associated disease characterized by chronic inflammation primarily driven by macrophages. The bulk of evidence has demonstrated the central role of epigenetic machinery in macrophage polarization to pro- (M1-like) or anti-inflammatory (M2-like) phenotype. An increasing number of epigenetic alterations and their modifiers involved in reprogramming macrophages by regulating DNA methylation or histone modifications (e.g., methylation, acetylation, and recently lactylation) have been identified. They may act to determine or skew the direction of macrophage polarization in AS lesions, thereby representing a promising target. Here we describe the current understanding of the epigenetic machinery involving macrophage polarization, to shed light on chronic inflammation-driving onset and progression of inflammaging-associated diseases, using AS as a prototypic example, and discuss the challenge for developing effective therapies targeting the epigenetic modifiers against these diseases, particularly highlighting a potential strategy based on epigenetically-governed repolarization from M1-like to M2-like phenotype.

Targeting epigenetic modifiers to reprogramme macrophages in non-resolving inflammation-driven atherosclerosis

Epigenomic and epigenetic research has been providing several new insights into a variety of diseases caused by non-resolving inflammation, including cardiovascular diseases. Atherosclerosis (AS) has long been recognized as a chronic inflammatory disease of the arterial walls, characterized by local persistent and stepwise accelerating inflammation without resolution, also known as uncontrolled inflammation. The pathogenesis of AS is driven primarily by highly plastic macrophages via their polarization to pro- or anti-inflammatory phenotypes as well as other novel subtypes recently identified by single-cell sequencing. Although emerging evidence has indicated the key role of the epigenetic machinery in the regulation of macrophage plasticity, the investigation of epigenetic alterations and modifiers in AS and related inflammation is still in its infancy. An increasing number of the epigenetic modifiers (e.g. TET2, DNMT3A, HDAC3, HDAC9, JMJD3, KDM4A) have been identified in epigenetic remodelling of macrophages through DNA methylation or histone modifications (e.g. methylation, acetylation, and recently lactylation) in inflammation. These or many unexplored modifiers function to determine or switch the direction of macrophage polarization via transcriptional reprogramming of gene expression and intracellular metabolic rewiring upon microenvironmental cues, thereby representing a promising target for anti-inflammatory therapy in AS. Here, we review up-to-date findings involving the epigenetic regulation of macrophages to shed light on the mechanism of uncontrolled inflammation during AS onset and progression. We also discuss current challenges for developing an effective and safe anti-AS therapy that targets the epigenetic modifiers and propose a potential anti-inflammatory strategy that repolarizes macrophages from pro- to anti-inflammatory phenotypes.

Modulation of Cell Surface Receptor Expression by Modified Vaccinia Virus Ankara in Leukocytes of Healthy and HIV-Infected Individuals

Viral vectors are increasingly used as delivery means to induce a specific immunity in humans and animals. However, they also impact the immune system, and it depends on the given context whether this is beneficial or not. The attenuated vaccinia virus strain modified vaccinia virus Ankara (MVA) has been used as a viral vector in clinical studies intended to treat and prevent cancer and infectious diseases. The adjuvant property of MVA is thought to be due to its capability to stimulate innate immunity. Here, we confirmed that MVA induces interleukin-8 (IL-8), and this chemokine was upregulated significantly more in monocytes and HLA-DR^bright dendritic cells (DCs) of HIV-infected patients on combined antiretroviral therapy (ART) than in cells of healthy persons. The effect of MVA on cell surface receptors is mostly unknown. Using mass cytometry profiling, we investigated the expression of 17 cell surface receptors in leukocytes after ex vivo infection of human whole-blood samples with MVA. We found that MVA downregulates most of the characteristic cell surface markers in particular types of leukocytes. In contrast, C-X-C motif chemokine receptor 4 (CXCR4) was significantly upregulated in each leukocyte type of healthy persons. Additionally, we detected a relative higher cell surface expression of the HIV-1 co-receptors C-C motif chemokine receptor 5 (CCR5) and CXCR4 in leukocytes of HIV-ART patients than in healthy persons. Importantly, we showed that MVA infection significantly downregulated CCR5 in CD4+ T cells, CD8+ T cells, B cells, and three different DC populations. CD86, a costimulatory molecule for T cells, was significantly upregulated in HLA-DR^bright DCs after MVA infection of whole blood from HIV-ART patients. However, MVA was unable to downregulate cell surface expression of CD11b and CD32 in monocytes and neutrophils of HIV-ART patients to the same extent as in monocytes and neutrophils of healthy persons. In summary, MVA modulates the expression of many different kinds of cell surface receptors in leukocytes, which can vary in cells originating from persons previously infected with other pathogens.

Impairment of hypoxia-induced angiogenesis by LDL involves a HIF-centered signaling network linking inflammatory TNFα and angiogenic VEGF

Hypoxia inducible factors (HIFs) mediate angiogenesis via up-regulation of various pro-angiogenic factors (particularly VEGF) in response to hypoxia. Here, we report that hypoxia unexpectedly induced robust production of the pro-inflammatory factor TNFα by endothelial cells (ECs), suggesting an autocrine loop that in turn activated HIFs via an NF-κB-dependent process, resulting in production of VEGF and thereby promotion of angiogenesis. In contrast, low-density lipoprotein (LDL) prevented expression of HIFs in ECs exposed to either hypoxia or TNFα, while knockdown of either HIF-1α or HIF-2α strikingly attenuated hypoxia-induced production of VEGF by ECs as well as EC colony formation and tube formation. Significantly, LDL attenuated hypoxia-induced angiogenesis by disrupting the TNFα/NF-κB/HIF/VEGF signaling cascade via down-regulation of the TNF receptor TNF-R1, rather than TNFα itself, and multiple key components of both canonical and non-canonical NF-κB pathways. By doing so, LDL was able to either inhibit or down-regulate a wide spectrum of HIF-dependent pro-angiogenic downstream targets and signals. Together, these findings argue existence of a self-regulatory TNFα/NF-κB/HIF/VEGF signaling network in ECs, which mediates and fine-tones angiogenesis, at least in response to hypoxia. They also suggest that LDL impairs angiogenesis by disrupting this network, which might represent a novel mechanism underlying anti-angiogenic property of LDL.

Leukemia-Associated Nup214 Fusion Proteins Disturb the XPO1-Mediated Nuclear-Cytoplasmic Transport Pathway and Thereby the NF-κB Signaling Pathway

Nuclear-cytoplasmic transport through nuclear pore complexes is mediated by nuclear transport receptors. Previous reports have suggested that aberrant nuclear-cytoplasmic transport due to mutations or overexpression of nuclear pore complexes and nuclear transport receptors is closely linked to diseases. Nup214, a component of nuclear pore complexes, has been found as chimeric fusion proteins in leukemia. Among various Nup214 fusion proteins, SET-Nup214 and DEK-Nup214 have been shown to be engaged in tumorigenesis, but their oncogenic mechanisms remain unclear. In this study, we examined the functions of the Nup214 fusion proteins by focusing on their effects on nuclear-cytoplasmic transport. We found that SET-Nup214 and DEK-Nup214 interact with exportin-1 (XPO1)/CRM1 and nuclear RNA export factor 1 (NXF1)/TAP, which mediate leucine-rich nuclear export signal (NES)-dependent protein export and mRNA export, respectively. SET-Nup214 and DEK-Nup214 decreased the XPO1-mediated nuclear export of NES proteins such as cyclin B and proteins involved in the NF-κB signaling pathway by tethering XPO1 onto nuclear dots where Nup214 fusion proteins are localized. We also demonstrated that SET-Nup214 and DEK-Nup214 expression inhibited NF-κB-mediated transcription by abnormal tethering of the complex containing p65 and its inhibitor, IκB, in the nucleus. These results suggest that SET-Nup214 and DEK-Nup214 perturb the regulation of gene expression through alteration of the nuclear-cytoplasmic transport system.

Butyrate regulates the expression of inflammatory and chemotactic cytokines in human acute leukemic cells during apoptosis

Butyrate is a histone deacetylase inhibitor implicated in many studies as a potential therapy for various forms of cancer. High concentrations of butyrate (>1.5mM) have been shown to activate apoptosis in several cancer cell lines including prostate, breast, and leukemia. Butyrate is also known to influence multiple signaling pathways that are mediators of cytokine production. The purpose of this study was to evaluate the impact of high concentrations of butyrate on the cancer microenvironment vis-à-vis apoptosis, cellular migration, and capacity to modulate cytokine expression in cancer cells. The results indicate that high concentrations of butyrate induced a 2-fold activation of caspase-3 and reduced cell viability by 60% in U937 leukemia cells. Within 24h, butyrate significantly decreased the levels of chemokines CCL2 and CCL5 in HL-60 and U937 cells, and decreased CCL5 in THP-1 leukemia cells. Differential effects were observed in treatments with valproic acid for CCL2 and CCL5 indicating butyrate-specificity. Many of the biological effects examined in this study are linked to activation of the AKT and MAPK signaling pathways; therefore, we investigated whether butyrate alters the levels of phosphorylated forms of these signaling proteins and how it correlated with the expression of chemokines. The results show that butyrate may partially regulate CCL5 production via p38 MAPK. The decrease in p-ERK1/2 and p-AKT levels correlated with the decrease in CCL2 production. These data suggest that while promoting apoptosis, butyrate has the potential to influence the cancer microenvironment by inducing differential expression of cytokines.

Histone deacetylase inhibitor (HDACI) mechanisms of action: emerging insights

Initially regarded as "epigenetic modifiers" acting predominantly through chromatin remodeling via histone acetylation, HDACIs, alternatively referred to as lysine deacetylase or simply deacetylase inhibitors, have since been recognized to exert multiple cytotoxic actions in cancer cells, often through acetylation of non-histone proteins. Some well-recognized mechanisms of HDACI lethality include, in addition to relaxation of DNA and de-repression of gene transcription, interference with chaperone protein function, free radical generation, induction of DNA damage, up-regulation of endogenous inhibitors of cell cycle progression, e.g., p21, and promotion of apoptosis. Intriguingly, this class of agents is relatively selective for transformed cells, at least in pre-clinical studies. In recent years, additional mechanisms of action of these agents have been uncovered. For example, HDACIs interfere with multiple DNA repair processes, as well as disrupt cell cycle checkpoints, critical to the maintenance of genomic integrity in the face of diverse genotoxic insults. Despite their pre-clinical potential, the clinical use of HDACIs remains restricted to certain subsets of T-cell lymphoma. Currently, it appears likely that the ultimate role of these agents will lie in rational combinations, only a few of which have been pursued in the clinic to date. This review focuses on relatively recently identified mechanisms of action of HDACIs, with particular emphasis on those that relate to the DNA damage response (DDR), and discusses synergistic strategies combining HDACIs with several novel targeted agents that disrupt the DDR or antagonize anti-apoptotic proteins that could have implications for the future use of HDACIs in patients with cancer.

Histone deacetylase inhibitors activate NF-kappaB in human leukemia cells through an ATM/NEMO-related pathway

Mechanisms underlying histone deacetylase inhibitor (HDACI)-mediated NF-kappaB activation were investigated in human leukemia cells. Exposure of U937 and other leukemia cells to LBH-589 induced reactive oxygen species (ROS) followed by single strand (XRCC1) and double strand (gamma-H2AX) DNA breaks. Notably, LBH-589 lethality was markedly attenuated by small interfering RNA (siRNA) knockdown of the DNA damage-linked histone, H1.2. LBH-589 triggered p65/RelA activation, NF-kappaB-dependent induction of Mn-SOD2, and ROS elimination. Interference with LBH-589-mediated NF-kappaB activation (e.g. in I kappaB alpha super-repressor transfected cells) diminished HDACI-mediated Mn-SOD2 induction and increased ROS accumulation, DNA damage, and apoptosis. The Mn-SOD2 mimetic TBAP (manganese(III)-tetrakis 4-benzoic acid porphyrin) prevented HDACI-induced ROS and NF-kappaB activation while dramatically attenuating DNA damage and cell death. In contrast, TRAF2 siRNA knockdown, targeting receptor-mediated NF-kappaB activation, blocked TNFalpha- but not HDACI-mediated NF-kappaB activation and lethality. Consistent with ROS-mediated DNA damage, LBH-589 exposure activated ATM (on serine 1981) and increased its association with NEMO. Significantly, siRNA NEMO or ATM knockdown blocked HDACI-mediated NF-kappaB activation, resulting in diminished MnSOD2 induction and enhanced oxidative DNA damage and cell death. In accord with the recently described DNA damage/ATM/NEMO pathway, SUMOylation site mutant NEMO (K277A or K309A) cells exposed to LBH-589 displayed diminished ATM/NEMO association, NEMO and p65/RelA nuclear localization/activation, and MnSOD2 up-regulation. These events were accompanied by increased ROS production, gamma-H2AX formation, and cell death. Together, these findings indicate that in human leukemia cells, HDACIs activate the cytoprotective NF-kappaB pathway through an ATM/NEMO/SUMOylation-dependent process involving the induction of ROS and DNA damage and suggest that blocking NF-kappaB activation via the atypical ATM/NEMO nuclear pathway can enhance HDACI antileukemic activity.

PCI-24781 induces caspase and reactive oxygen species-dependent apoptosis through NF-kappaB mechanisms and is synergistic with bortezomib in lymphoma cells

PURPOSE

We investigated the cytotoxicity and mechanisms of cell death of the broad-spectrum histone deacetylase (HDAC) inhibitor PCI-24781, alone and combined with bortezomib in Hodgkin lymphoma and non-Hodgkin lymphoma cell lines and primary lymphoproliferative (CLL/SLL) cells.

EXPERIMENTAL DESIGN

Apoptosis, mitochondrial membrane potential, cell cycle analysis, and reactive oxygen species (ROS) were measured by flow cytometry, whereas caspase activation was determined by Western blot. Nuclear factor kappaB (NF-kappaB)-related mRNAs were quantified by reverse transcription-PCR, NF-kappaB-related proteins by Western blotting, and NF-kappaB DNA-binding activity by electromobility shift assay. Finally, gene expression profiling was analyzed.

RESULTS

PCI-24781 induced concentration-dependent apoptosis that was associated with prominent G(0)/G(1) arrest, decreased S-phase, increased p21 protein, and increased ROS in Hodgkin lymphoma and non-Hodgkin lymphoma cell lines. Dose-dependent apoptosis with PCI-24781 was also seen among primary CLL/SLL cells. PCI-24781-induced apoptosis was shown to be ROS- and caspase-dependent. Combined PCI-24781/bortezomib treatment resulted in strong synergistic apoptosis in all non-Hodgkin lymphoma lines (combination indices, 0.19-0.6) and was additive in Hodgkin lymphoma and primary CLL/SLL cells. Further, PCI-24781/bortezomib resulted in increased caspase cleavage, mitochondrial depolarization, and histone acetylation compared with either agent alone. Gene expression profiling showed that PCI-24781 alone significantly down-regulated several antioxidant genes, proteasome components, and NF-kappaB pathway genes, effects that were enhanced further with bortezomib. Reverse transcription-PCR confirmed down-regulation of NF-kappaB1 (p105), c-Myc, and IkappaB-kinase subunits, where NF-kappaB DNA binding activity was decreased.

CONCLUSION

We show that PCI-24781 results in increased ROS and NF-kappaB inhibition, leading to caspase-dependent apoptosis. We also show that bortezomib is synergistic with PCI-24781. This combination or PCI-24781 alone has potential therapeutic value in lymphoma.

Nuclear organization of PML bodies in leukaemic and multiple myeloma cells

The nuclear arrangement of promyelocytic leukaemia nuclear bodies (PML NBs) was studied in vitro after the cell treatment by clinically used agents such as all-trans retinoic acid (RA) in human leukaemia and cytostatics or gamma radiation in multiple myeloma cells. In addition, the influence of phorbol ester (PMA) on PML NBs formation was analyzed. A reduced number of PML bodies, which led to relocation of PML NBs closer to the nuclear interior, mostly accompanied RA- and PMA-induced differentiation. Centrally located PML NBs were associated with transcriptional protein RNAP II and SC35 regions, which support importance of PML NBs in RNA processing that mostly proceeds within the nuclear interior. Conversely, the quantity of PML NBs was increased after cytostatic treatment, which caused re-distribution of PML NBs closer to the nuclear envelope. Here we showed correlations between the number of PML NBs and average Centre-to-PML distances. Moreover, a number of cells in S phase, especially during differentiation, influenced number of PML NBs. Studying the proteins involved in PML compartment, such as c-MYC, cell-type specific association of c-MYC and the PML NBs was observed in selected leukaemic cells undergoing differentiation, which was accompanied by c-MYC down-regulation.

Vorinostat synergistically potentiates MK-0457 lethality in chronic myelogenous leukemia cells sensitive and resistant to imatinib mesylate

Interactions between the dual Bcr/Abl and aurora kinase inhibitor MK-0457 and the histone deacetylase inhibitor vorinostat were examined in Bcr/Abl(+) leukemia cells, including those resistant to imatinib mesylate (IM), particularly those with the T315I mutation. Coadministration of vorinostat dramatically increased MK-0457 lethality in K562 and LAMA84 cells. Notably, the MK-0457/vorinostat regimen was highly active against primary CD34(+) chronic myelogenous leukemia (CML) cells and Ba/F3 cells bearing various Bcr/Abl mutations (ie, T315I, E255K, and M351T), as well as IM-resistant K562 cells exhibiting Bcr/Abl-independent, Lyn-dependent resistance. These events were associated with inactivation and down-regulation of wild-type (wt) and mutated Bcr/Abl (particularly T315I). Moreover, treatment with MK-0457 resulted in accumulation of cells with 4N or more DNA content, whereas coadministration of vorinostat markedly enhanced aurora kinase inhibition by MK-0457, and preferentially killed polyploid cells. Furthermore, vorinostat also interacted with a selective inhibitor of aurora kinase A and B to potentiate apoptosis without modifying Bcr/Abl activity. Finally, vorinostat markedly induced Bim expression, while blockade of Bim induction by siRNA dramatically diminished the capacity of this agent to potentiate MK-0457 lethality. Together, these findings indicate that vorinostat strikingly increases MK-0457 activity against IM-sensitive and -resistant CML cells through inactivation of Bcr/Abl and aurora kinases, as well as by induction of Bim.

The novel histone deacetylase inhibitor BML-210 exerts growth inhibitory, proapoptotic and differentiation stimulating effects on the human leukemia cell lines

Histone deacetylase inhibitors have a potent role in the strategy for the treatment of leukemias. BML-210 (N-(2-Aminophenyl)-N' phenyloctanol diamine) is the novel histone deacetylase inhibitor, and its mechanism of action has not been characterized. In this study, we examined the in vitro effects of BML-210 on the human leukemia cell lines (NB4, HL-60, THP-1, and K562). We found that BML-210 inhibits the growth of all cell lines and promotes apoptosis in a dose- and time-dependent manner. BML-210 alone induces HL-60 and K562 cell differentiation (up to 30%) to granulocytes and erythrocytes, respectively, and in combination with differentiation agents - all-trans retinoic acid and hemin, markedly potentates it. Those treatments cause G1 arrest and histone H4 acetylation, affects transcription factor NF-kappaB and Sp1 binding activity to their consensus sequences, the p21 or the FasL promoters, and influences expression of Sp1, NF-kappaB, p21 and FasL. These findings suggest that BML-210 could be a promising antileukemic agent to induce apoptosis and to modulate differentiation through the modulation of histone acetylation and gene expression.

Regulation of progranulin expression in myeloid cells

Progranulin (pgrn; granulin-epithelin precursor, PC-cell-derived growth factor, or acrogranin) is a multifunctional secreted glycoprotein implicated in tumorigenesis, development, inflammation, and repair. It is highly expressed in macrophage and monocyte-derived dendritic cells. Here we investigate its regulation in myeloid cells. All-trans retinoic acid (ATRA) increased pgrn mRNA levels in myelomonocytic cells (CD34(+) progenitors; monoblastic U-937; monocytic THP-1; progranulocytic HL-60; macrophage RAW 264.7) but not in nonmyeloid cells tested. Interleukin-4 impaired basal expression of pgrn in U-937. Differentiation agents DMSO, and, in U-937 only, phorbol ester [phorbol 12-myristate,13-acetate (PMA)] elevated pgrn mRNA expression late in differentiation, suggestive of roles for pgrn in more mature terminally differentiated granulocyte/monocytes rather than during growth or differentiation. The response of pgrn mRNA to ATRA differs in U-937 and HL-60 lineages. In U-937, ATRA and chemical differentiation agents greatly increased pgrn mRNA stability, whereas, in HL-60, ATRA accelerated pgrn mRNA turnover. The initial upregulation of pgrn mRNA after stimulation with ATRA was independent of de novo protein synthesis in U-937 but not HL-60. Chemical blockade of nuclear factor-kappaB (NF-kappaB) activation impaired ATRA-stimulated pgrn expression in HL-60 but not U-937, whereas in U-937 it blocked PMA-induced pgrn mRNA expression, suggestive of cell-specific roles for NF-kappaB in determining pgrn mRNA levels. We propose that: 1) ATRA regulates pgrn mRNA levels in myelomonocytic cells; 2) ATRA acts in a cell-specific manner involving the differential control of mRNA stability and differential requirement for NF-kappaB signaling; and 3) elevated pgrn mRNA expression is characteristic of more mature cells and does not stimulate differentiation.

Potentiation of the anticancer effect of valproic acid, an antiepileptic agent with histone deacetylase inhibitory activity, by the kinase inhibitor Staurosporine or its clinically relevant analogue UCN-01

Histone deacetylase inhibitors (HDACIs) are novel anticancer agents with potent cytotoxicity against a wide range of malignancies. We have previously demonstrated that either Calphostin C (CC) (a protein kinase C (PKC) inhibitor) or Parthenolide (an NF-kappaB inhibitor) abrogates HDACI-induced transcriptional activation of NF-kappaB and p21, which is associated with profound potentiation of HDACI-mediated induction of apoptosis. Valproic acid (VA), a commonly used antiepileptic agent, has recently been shown to be an HDACI. This study was aimed to evaluate the anticancer property of VA in thoracic cancer cells and the development of clinically relevant strategies to enhance VA-mediated induction of apoptosis using kinase inhibitors Staurosporine (STP) or its analogue UCN-01. Treating cultured thoracic cancer cells with VA (0.62-10.0 mM) resulted in significant cell line- and dose-dependent growth inhibition (IC(50) values: 4.1-6.0 mM) and cell cycle arrest at G1/S checkpoint with profound accumulation of cells at G0/G1 phase but little induction of apoptosis. Valproic acid, being an HDACI, caused significant dose-dependent accumulation of hyperacetylated histones, following 24 h of treatment. Valproic acid-mediated 5-20-fold upregulation of transcriptional activity of NF-kappaB was substantially (50-90%) suppressed by cotreatment with CC, STP or UCN-01. Whereas minimal death (<20%) was observed in cells treated with either VA (1.0 or 5.0 mM) alone or kinase inhibitors alone, 60-90% of cells underwent apoptosis following exposure to combinations of VA+kinase inhibitors. Kinase inhibitor-mediated suppression of NF-kappaB transcriptional activity played an important role in sensitising cancer cells to VA as direct inhibition of NF-kappaB by Parthenolide drastically synergised with VA to induce apoptosis (VA+Parthenolide: 60-90% compared to <20% following single-drug treatments). In conclusion, VA, a well-known antiepileptic drug, has mild growth-inhibitory activity on cultured cancer cells. The weak VA-mediated induction of apoptosis of thoracic cancer cells can be profoundly enhanced either by Parthenolide, a pharmacologic inhibitor of NF-kappaB, or by UCN-01 a kinase inhibitor that has already undergone phase I clinical development. Combinations of VA with either a PKC inhibitor or an NF-kappaB inhibitor are promising novel molecularly targeted therapeutics for thoracic cancers.

G1/S arrest induced by histone deacetylase inhibitor sodium butyrate in E1A + Ras-transformed cells is mediated through down-regulation of E2F activity and stabilization of beta-catenin

Tumor cells are often characterized by a high and growth factor-independent proliferation rate. We have previously shown that REF cells transformed with oncogenes E1A and c-Ha-Ras do not undergo G(1)/S arrest of the cell cycle after treatment with genotoxic factors. In this work, we used sodium butyrate, a histone deacetylase inhibitor, to show that E1A + Ras transformants were able to stop proliferation and undergo G(1)/S arrest. Apart from inducing G(1)/S arrest, sodium butyrate was shown to change expression of a number of cell cycle regulatory genes. It down-regulated cyclins D1, E, and A as well as c-myc and cdc25A and up-regulated the cyclin-kinase inhibitor p21(waf1). Accordingly, activities of cyclin E-Cdk2 and cyclin A-Cdk2 complexes in sodium butyrate-treated cells were decreased substantially. Strikingly, E2F1 expression was also down-modulated at the levels of gene transcription, the protein content, and the E2F transactivating capability. To further study the role of p21(waf1) in the sodium butyrate-induced G(1)/S arrest and the E2F1 down-modulation, we established E1A + Ras transformants from mouse embryo fibroblast cells with deletion of the cdkn1a (p21(waf1)) gene. Despite the absence of p21(waf1), sodium butyrate-treated mERas transformants reveal a slightly delayed G(1)/S arrest as well as down-modulation of E2F1 activity, implying that the observed effects are mediated through an alternative p21(waf1)-independent signaling pathway. Subsequent analysis showed that sodium butyrate induced accumulation of beta-catenin, a downstream component of the Wnt signaling. The results obtained indicate that the antiproliferative effect of histone deacetylase inhibitors on E1A + Ras-transformed cells can be mediated, alongside other mechanisms, through down-regulation of E2F activity and stabilization of beta-catenin.

Differentiation of androgen-independent prostate cancer PC-3 cells is associated with increased nuclear factor-kappaB activity

Recently, we have reported that inosine 5'-monophosphate dehydrogenase inhibitors, such as mycophenolic acid (MPA), induce the differentiation of PC-3 cells, which are derived from a human androgen-independent prostate cancer, into cells with a phenotype resembling maturing prostate secretory cells. Here, we describe such differentiation induced by the histone deacetylase inhibitor tributyrin. The maturation was defined by cytoplasmic vacuole production and induction of CD10, CD46, CD55, GRP78, keratin 17, and zinc-alpha-2-glycoprotein. To identify additional genes associated with tributyrin-induced PC-3 cell differentiation and to gain some insight into the mechanism that underlies this differentiation, we have, by means of microarray analyses, compared tributyrin-induced gene expression patterns with those of MPA, which initiates PC-3 cell differentiation by a dissimilar mode of action. We suggested that genes induced by both tributyrin and MPA would be most likely associated with differentiation rather than with the unique action of each particular inducer. Our results indicated that tributyrin or MPA induced the expression of a large number of common genes, including genes known or assumed to be NF-kappaB dependent. The NF-kappaB dependency of a group of these genes, which included the PC-3 cell differentiation marker keratin 17, was confirmed by using two common NF-kappaB activation inhibitors, Bay11-082 and TMB-8, and p65 subunit of NF-kappaB complex specific small interfering RNA. Taken together, our results implicate both NF-kappaB-dependent and NF-kappaB-independent genes in the processes leading to PC-3 cell differentiation induced by tributyrin and MPA.

Synergistic interactions between MEK1/2 and histone deacetylase inhibitors in BCR/ABL+ human leukemia cells

Interactions between the histone deacetylase inhibitor SAHA and the pharmacologic MEK1/2 inhibitor PD184352 were examined in Bcr/Abl+ human leukemia cells. Coadministration of minimally toxic concentrations of SAHA (or sodium butyrate) and PD184352 (or U0126) resulted in a synergistic increase in mitochondrial damage, caspase activation, and apoptosis in K562 and LAMA 84 cells. Similar interactions were observed in CD34+ cells from two patients with CML and in imatinib mesylate-resistant K562 cells but not in normal human CD34+ bone marrow cells. These events were associated with a marked increase in ROS generation, inactivation of ERK and Akt, downregulation of p21CIP1, Bcr/Abl, and cyclin D1, and activation of JNK. Of these events, ROS generation, ERK inactivation, and cytochrome c/AIF release were largely caspase-independent, whereas the other phenomena displayed varying degrees of caspase-dependence. Using pharmacologic and genetic approaches, generation of ROS, p21CIP1 downregulation, and inactivation of Akt and MEK were found to play significant functional roles in SAHA/PD184352-mediated lethality, whereas JNK activation and Raf-1 downregulation were determined to represent secondary events. These findings indicate that interruption of the MEK/ERK pathway substantially lowers the threshold for HDAC inhibitor-mediated oxidative injury, mitochondrial dysfunction, and apoptosis, suggesting that this approach warrants further examination in Bcr/Abl+-related malignancies.

Histone deacetylase inhibitors in clinical development

In addition to a variety of other novel agents, interest in histone deacetylase inhibitors (HDACIs) as antineoplastic drugs has recently accelerated and increasing numbers of these compounds have entered clinical trials in humans. HDACIs represent a prototype of molecularly targeted agents that perturb signal transduction, cell cycle-regulatory and survival-related pathways. Newer generation HDACIs have been introduced into the clinical arena that are considerably more potent on a molar basis than their predecessors and are beginning to show early evidence of activity, particularly in hematopoietic malignancies. In addition, there is an increasing appreciation of the fact that HDACIs may act through mechanisms other than induction of histone acetylation and, as in the case of other molecularly-targeted agents, it is conceivable that the ultimate role of HDACIs in cancer therapy will be as modulators of apoptosis induced by other cytotoxic agents. One particularly promising strategy involves attempts to combine HDACIs with other novel agents to promote tumour cell differentiation or apoptosis. The present review focuses on recent insights into the mechanisms by which HDACIs exert their anticancer effects, either alone or in combination with other compounds, as well as attempts to translate these findings into the clinic.

Blocking anti-apoptosis as a strategy for cancer chemotherapy: NF-kappaB as a target

Critical processes underlying cancers must be better understood to develop strategies for treatment and prevention. A chemotherapeutic strategy is proposed that is based upon re-establishment, with a drug, of nullified programmed cell death (apoptosis) in cancer cells, which to survive have mutated to block apoptosis. A chemotherapy that is specific against tumors implanted in mice demonstrated the feasibility of this principle. This therapy is specific because it affects a process unique to cancer cells. It also has the advantage of killing these cells, in contrast to reversibly blocking their proliferation. The anti-apoptotic transcription factor NF-kappaB provides a potential therapeutic target in estrogen receptor negative (ER-) breast cancers that over-express the epidermal growth factor family of receptors (EGFR). Further investigations of the pathways utilize dominant negative protein inhibitory peptide, and small inhibitory RNAs (siRNAs) to block the production of relevant enzymes.

Synergistic induction of oxidative injury and apoptosis in human multiple myeloma cells by the proteasome inhibitor bortezomib and histone deacetylase inhibitors

PURPOSE

The purpose of this study was to examine interactions between the proteasome inhibitor bortezomib (Velcade) and the histone deacetylase (HDAC) inhibitors sodium butyrate and suberoylanilide hydroxamic acid in human multiple myeloma (MM) cells that are sensitive and resistant to conventional agents.

EXPERIMENTAL DESIGN

MM cells were exposed to bortezomib for 6 h before the addition of HDAC inhibitors (total, 26 h), after which reactive oxygen species (ROS), mitochondrial dysfunction, signaling and cell cycle pathways, and apoptosis were monitored. The functional role of ROS generation was assessed using the free radical scavenger N-acetyl-l-cysteine.

RESULTS

Preincubation with a subtoxic concentration of bortezomib markedly sensitized U266 and MM.1S cells to sodium butyrate- and suberoylanilide hydroxamic acid-induced mitochondrial dysfunction; caspase 9, 8, and 3 activation; and poly(ADP-ribose) polymerase degradation; resulting in synergistic apoptosis induction. These events were associated with nuclear factor kappaB inactivation, c-Jun NH(2)-terminal kinase activation, p53 induction, and caspase-dependent cleavage of p21(CIP1), p27(KIP1), and Bcl-2, as well as Mcl-1, X-linked inhibitor of apoptosis, and cyclin D1 down-regulation. The bortezomib/HDAC inhibitor regimen markedly induced ROS generation; moreover, apoptosis and c-Jun NH(2)-terminal kinase activation were attenuated by N-acetyl-l-cysteine. Dexamethasone- or doxorubicin-resistant MM cells failed to exhibit cross-resistance to the bortezomib/HDAC inhibitor regimen, nor did exogenous interleukin 6 or insulin-like growth factor I block apoptosis induced by this drug combination. Finally, bortezomib/HDAC inhibitors induced pronounced lethality in primary CD138(+) bone marrow cells from MM patients, but not in the CD138(-) cell population.

CONCLUSIONS

Sequential exposure to bortezomib in conjunction with clinically relevant HDAC inhibitors potently induces mitochondrial dysfunction and apoptosis in human MM cells through a ROS-dependent mechanism, suggesting that a strategy combining these agents warrants further investigation in MM.

Bortezomib and flavopiridol interact synergistically to induce apoptosis in chronic myeloid leukemia cells resistant to imatinib mesylate through both Bcr/Abl-dependent and -independent mechanisms

Interactions between the cyclin-dependent kinase (CDK) inhibitor flavopiridol and the proteasome inhibitor bortezomib were examined in Bcr/Abl(+) human leukemia cells. Coexposure of K562 or LAMA84 cells to subtoxic concentration of flavopiridol (150-200 nM) and bortezomib (5-8 nM) resulted in a synergistic increase in mitochondrial dysfunction and apoptosis. These events were associated with a marked diminution in nuclear factor kappaB (NF-kappaB)/DNA binding activity; enhanced phosphorylation of SEK1/MKK4 (stress-activated protein kinase/extracellular signal-related kinase 1/mitogen-activated protein kinase kinase 4), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK); down-regulation of Bcr/Abl; and a marked reduction in signal transducer and activator of transcription 3 (STAT3) and STAT5 activity. In imatinib mesylate-resistant K562 cells displaying increased Bcr/Abl expression, bortezomib/flavopiridol treatment markedly increased apoptosis in association with down-regulation of Bcr/Abl and BclxL, and diminished phosphorylation of Lyn, Hck, CrkL, and Akt. Parallel studies were performed in imatinib mesylate-resistant LAMA84 cells exhibiting reduced expression of Bcr/Abl but a marked increase in expression/activation of Lyn and Hck. Flavopiridol/bortezomib effectively induced apoptosis in these cells in association with Lyn and Hck inactivation. The capacity of flavopiridol to promote bortezomib-mediated Bcr/Abl down-regulation and apoptosis was mimicked by the positive transcription elongation factor-b (P-TEFb) inhibitor DRB (5,6-dichloro 1-beta-d-ribofuranosylbenzinida-sole). Finally, the bortezomib/flavopiridol regimen also potently induced apoptosis in Bcr/Abl(-) human leukemia cells. Collectively, these findings suggest that a strategy combining flavopiridol and bortezomib warrants further examination in chronic myelogenous leukemia and related hematologic malignancies.